The DVD, HD DVD and Blu-ray specifications currently define mechanisms for seamlessly switching among multiple parallel A/V streams. However, in each case, the audio and sub-picture content of the streams is restricted to be bit-for-bit identical among all of the streams. This prevents any potential damage to audio speakers that could result from signal spikes caused by differences in the audio data from one A/V stream to another, and also reduces the restrictions regarding organization of such data within each multiplexed A/V stream. However, these restrictions also greatly limit the range of applications for which the seamless multi-angle feature may be used.
The development of the DVD followed the development of the Compact Disk (CD) in an effort to achieve sufficient storage capacity for large video files to enable a single disc to carry a full length motion picture, albeit compressed using a compression technique such as the Moving Picture Expert Group compression (MPEG) technique. Since its first introduction in the mid 1990s, the DVD has proliferated, becoming the preferred medium of choice for wide scale distribution of motion picture and video content to consumers. Similar optical disc formats for delivery of higher quality and greater amounts of audiovisual content have been developed as planned successors to DVD. Two of the most prominent formats are known as HD DVD and BD.
Present day DVDs, HD DVDS, and BDs typically include at least one, and usually several A/V streams in parallel synchronism to each other. Often such A/V streams include different recordings of the same scene shot from a different angle. Hence, such different A/V streams are often referred to as “angles”. Selection of different angles (i.e., different streams) occurs through a process known as “multi-angle navigation” whereby a viewer selects a desired angle by selecting an associated icon on a display screen. The DVD, HD DVD, and BD specifications adopted by the manufacturers of these discs and associated playback devices define a process known as “multi-angle video” whereby a content author can define as many as nine concurrent A/V streams, any one of which can appear on a display screen at any time. During playback, the viewer can switch seamlessly among a set of synchronized A/V streams by actuating a command via a button on a DVD, HD DVD, or BD player or on the remote control device for such player; this form of multi-angle navigation is known as seamless multi-angle. However, under known format specifications and implementations of currently available DVD, HD DVD, and BD authoring tools, audio and sub-picture data stored in each A/V stream remains identical. That is, only different video data is allowed between angles. Sub-picture data describes the rendering of buttons, subtitles, and other graphical elements displayed over video. This results both in an inability to automatically present different audio and sub-picture content when a parallel A/V stream is selected and also leads to redundant copies of audio and sub-picture data being stored on the delivery medium, limiting space for other content.
A/V streams are constituted at a basic level of data packets for the sub-streams (audio, video, and sub-picture) which are joined together in short units which, when read sequentially, comprise the presented stream. In DVD-Video, these fundamental data units are known as Video Object Units, or VOBUs, and each include about 0.4 to 1 second of presentation data. In HD DVD-Video, these are known as EVOBUs. The terms VOBUs and EVOBUs may be used interchangeably herein for illustrative purposes. When multiple A/V streams are presented in parallel, each stream collects one or more VOBUs into an Interleave Unit, or ILVU, which are synchronized with ILVUs for other parallel A/V streams based on the video presentation time. Thus, when a new stream is selected, the data from the current ILVU plays until the end of the ILVU and the ILVU for the new stream is presented seamlessly at that time. In this way, seamless presentation of video is assured.
BD refers to a similar combination of packets using different terminology, namely Transport Stream (TS). BD does not limit the duration of presentation data in the unit, using instead of ILVUs, angle change points in each TS to mark points at which streams can be changed while ensuring video continuity.
Audio, video, and sub-picture packets in VOBUs, TS, RTP or other packetized multimedia formats are all typically marked with a first type of timestamp indicating when they should be delivered for decoding and a second type of timestamp indicating when they should be presented. In the case of VOBUs, the delivery timestamps are encoded in the “system_clock_reference” as defined in ISO/IEC13818-1. In the case of Transport Streams (TSs), delivery timestamps are typically called “arrival_timestamps” as defined in some of the specifications derived from ISO/IEC 13818-1. As used herein, the term “arrival_timestamp” collectively refers to the delivery timestamp in VOBUs and TSs. The presentation timestamps are the usual PTSs as defined in ISO/IEC13818-1.
Due to different buffering models and decoder designs, non-video packets in a single VOBU (or at an angle change point marker in a TS) may not all refer to similar presentation times. For example, an audio packet may refer to presentation time 8, whereas a video packet may refer to presentation time 4, the audio packet for presentation time 4 having been delivered from a previous VOBU. When audio and sub-picture/subtitle data are identical between VOBUs in ILVUs (or between TSs) for different A/V streams in a parallel presentation, switching ILVUs or TSs has no effect on audio, sub-picture/subtitle, and video synchronization or correspondence/synchronization. However, when audio and sub-picture data packets differ between VOBUs or TSs for different A/V streams, a case could occur where audio or sub-picture/subtitle packets corresponding to the presentation time of the video from the new VOBU or TS have already been delivered from a previous VOBU or TS, resulting in audio or sub-picture/subtitle presentation that, while presented at the proper time, is out of correspondence/synchronization with the current context.
Thus, there exists a need for a method of storing data in a way that audio and sub-picture data are contextually different in parallel, synchronized A/V streams playing from any one of these optical disc formats and also maintain stream continuity as well as synchronization with video data as the viewer interactively selects different A/V streams during the presentation.